At present, the dominant methods for fabricating liquid crystal display devices (LCD) and panels are the methods based on amorphous silicon (a-Si) thin film transistor (TFT) technologies. Using these technologies, high quality image displays of substantial size can be fabricated using low temperature processes. As will be understood by those skilled in the art, conventional LCD devices typically include a transparent (e.g., glass) substrate with an array of thin film transistors thereon, pixel electrodes, orthogonal gate and data lines, a color filter substrate and liquid crystal material between the transparent substrate and the color filter substrate.
Referring now to FIGS. 1A-1E, a method of forming a TFT-LCD display device according to the prior art will be described. Referring to FIG. 1A, an amorphous silicon layer is deposited to a predetermined thickness on a transparent substrate 2 such as glass substrate by a chemical vapor deposition (CVD) method, resulting in a semiconductor layer used as an active layer. Then, the semiconductor layer is crystallized by irradiating it with a laser for a predetermined number of pulses, and then the semiconductor layer is patterned by a first photolithography process to form a semiconductor layer pattern 6. A doped polysilicon layer or metal layer may be deposited and then patterned to form a reinforcement layer 4 as shown in FIG. 1A, before the semiconductor layer pattern 6 is formed.
Referring to FIG. 1B, an insulation layer is deposited on the resultant structure having the semiconductor layer pattern 6 to form a gate insulation layer 8, and then a region in which a storage capacitor is to be formed is defined by a second photolithography process. Then, impurity ions are implanted into the defined region of the semiconductor layer by an ion shower doping method, resulting in a doped semiconductor layer pattern 6a in which the storage capacitor is to be formed. Then, a gate metal such as aluminum (Al) is deposited on the resultant structure and then the third photolithography process is performed to form a gate electrode 10 and an upper electrode 12 of the storage capacitor.
Referring to FIG. 1C, an N-channel TFT region is defined by a fourth photolithography process and then N.sup.+ impurities are implanted on the defined region by the ion shower doping method, resulting in an N.sup.+ -doped semiconductor layer pattern 14. Then, a P-channel TFT region is defined by a fifth photolithography process, and then P.sup.+ impurities are doped on the defined P-channel TFT region by the general ion shower doping method, resulting in a P.sup.+ -doped semiconductor layer pattern (not shown). Subsequently, a laser beam is irradiated on the resultant structure to activate the doped semiconductor layer pattern, resulting in a source/drain 14 of the TFT. Here, the undoped semiconductor layer 6 below the gate electrode 10 becomes a channel region of the TFT.
Referring to FIG. 1D, an insulation layer is deposited on the resultant structure having the source/drain 14 to a predetermined thickness to form an interlayer dielectric (ILD) film 16. The ILD film 16 is partially etched by a sixth photolithography process to form a contact hole. Then, a metal layer such as Al is deposited on the resultant structure having the contact hole, and then patterned by a seventh photolithography process to form a data line 20 and a metal layer pattern 18 for a pixel electrode. Referring to FIG. 1E, an insulation layer is deposited on the resultant structure having the data line 20 and the metal layer pattern 18 for the pixel electrode 18 to form a passivation layer 22. Then, the passivation layer 22 is patterned by an eighth photolithography process to form a via hole partially exposing the metal layer pattern 18 for the pixel electrode. Then, a transparent conductive layer such as indium tin oxide (ITO) is deposited on the resultant structure and then patterned by a ninth photolithography process to form a pixel electrode 24.
However, the above-described conventional method for manufacturing the TFT-LCD has the following disadvantages. First, contact resistance is typically high since the thickness of the semiconductor layer used as the active layer is thin. Thus, in order to reduce the contact resistance, the reinforcement layer 4 (see FIG. 1A) is formed on a contact formation region. However, the method for forming the reinforcement layer is complicated and also increases the number of masks. Second, since the step for irradiating with a laser beam is performed after the deposition of the amorphous silicon layer and the ion shower doping process, productivity is low. Third, since about 9-10 photolithography steps are required, manufacturing costs are high.